The present invention relates generally to a drilling bucket for excavating the ground on the earth drill method or the like and, more particularly, to an automatic evacuation drilling bucket which can automatically evacuate earth and sand received therein.
The earth drill method is well known, which is one of methods of substructure work wherein a drilling bucket is used to excavate the ground so as to form a hole, earth and sand due to excavation being received therein for evacuation on the ground. FIGS. 13-15 show one of drilling buckets for use in the earth drill method which is disclosed, for example, in JP-B2-59917. Referring to FIG. 13, a drive shaft member, designated generally by reference numeral 101, is connected to a kelly-bar (not shown), and splined to a follower 103 arranged to a support frame portion 102a of a bucket main body 102. Referring also to FIG. 14, an operating arm 104 is arranged to the drive shaft member 101, whereas an osculating arm 105 is disposed opposite to the operating arm 104 to be capable of coming in contact therewith, and it is integrally formed with an operating shaft 106 arranged to the bucket main body 102. Arranged to the operating shaft 106 at its lower end is a stop 107 which is detachably engaged with a receiver 109 of a bottom cover 108 which is mounted to the bucket main body 102 in a manner to be capable of opening and closing operation.
Referring to FIGS. 14 and 15, wherein the drive shaft member 101 is rotated by the kelly-bar in the direction of arrow A in FIG. 14 or in the normal direction, earth and sand are excavated by the bucket main body 102, and received within the bucket main body 102 through openings of the bottom cover 108. When evacuating earth and sand within the bucket main body 102 on the ground, the kelly-bar is rotated in the direction opposite to that of arrow A or the reverse direction. Then, due to presence of a play 110 interposed between the drive shaft member 101 and the follower l03 as shown in FIG. 15, the operating arm 104 is rotated from the position as indicated by a fully drawn line to the position as indicated by a one-dotted chain line in FIG. 14, thus rotating the osculating arm 105. At the same time, the operating shaft 106 is rotated, so that the stop 107 is disengaged with the receiver 109 to open the bottom cover 108, evacuating earth and sand within the bucket main body 102. Additionally, also when the drive shaft member 101 is rotated by the kelly-bar in the direction of arrow A in FIG. 14 for quick stoppage, the same operation is made, evacuating earth and sand within the bucket main body 101.
As to the prior art automatic evacuation drilling bucket, when the drive shaft member 101 is rotated in the normal direction to excavate the ground, the operating arm 104 fails to come in contact with the osculating arm 105, so that the operating shaft 106 is not rotated to open the bottom cover 108. However, if the drive shaft member 101 becomes incapable of rotation by encountering in the ground obstacles such as a big rubble, a driftwood, an old pile, a concrete fragment, or that the bucket main body 102 is locked in the hole as excavate by a wall thereof which overhangs the bucket main body 102 due to a soft bed, the drive shaft member 101 may be obliged to rotate in the reverse direction. Then, the operating arm 104 comes in contact with the osculating arm 105 to rotate the operating shaft 106, opening the bottom cover 108. If the bottom cover 108 is opened in the holes as excavated, it functions as an anchor, resulting in difficult lifting of the bucket main body 102 from the hole.
It is, therefore, an object of the present invention to provide an automatic evacuation drilling bucket wherein a bottom cover fails to be opened even when a drive shaft member is rotated in the reverse direction, or with a bucket being suspended.